The report describes the progress of a program to measure the acoustic impedance of a burning solid propellant. The analytical treatment to compensate for the introduction of exhaust ports in the sound chamber body is presented. Specific impedance measurements for JohnsManville Airacoustic using various test chambers are reported. Impedance measurements at elevated pressures are discussed. At present, passive tests have been conducted at 14.7, 500 and 1,000 psi to establish the test procedure and acceptability of the data in various modified sound chambers. The reduced data at one atmosphere confirm the acceptability of the method. Data reduction at 500 and 1,000 psi is now being performed. Propellant samples were fired in some of these chambers to allow the measurement of pressure rise upon ignition. A supplementary bibliography of applicable references is included as an appendix to this report.

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